It is common procedure either in large-scale reforestation projects or in large-scale farming operations for crops and the like, for germinating and growing seedlings in containers till such time they are ready to be transplanted in the field. Often the seedlings are started from seeds in a growth medium and grown in a controlled atmosphere such as in a greenhouse till the seedlings reach a desired size. In operations involving large numbers of seedlings, it is desirable to have arrangements wherein several seedlings can be germinated and grown in a suitable large container which has facilities for easily transplanting individual seedlings into the field in an easy and convenient manner. It is expedient to devise arrangements wherein the required facilities for the growth of the seedlings are best provided, and wherein at the same time handling and rehandling of the seedlings with root lumps are curtailed to the minimum.
It is found from experience that when the growth medium surrounding the root structure of each seedling is in a very wet condition, the roots are liable to easy tearing and damage. The possibility of the root lumps being undesirably wet at the time of transplanting does occur in seedling arrangements which use a plurality of pot-like cells forming several containers with closed bottoms, where there is no provision for drainage of excess water.
It is equally important to ensure that the seedling arrangement offers sufficient facility and convenience to dislodge each seedling together with its root lump and growth medium in such a manner that detrimental separation of the growth medium from the roots does not occur at the time of transplantation. It is essential especially in reforestation projects to ensure that the survival chances of replanted seedlings are high, and root separation from the growth medium during transplanting is certainly to be avoided.
The geometry and disposition of the individual cells per se have a profound effect on the manner in which the roots are guided and distributed in the growth medium. If adjacent cells in a seedling unit are too close and do not provide any barriers to prevent roots of one seedling from approaching the roots of an adjacent seedling, the roots will invariably get tangled and cause problems when the seedlings are lifted out of their cells. If, on the other hand, a barrier such as a substantially cylindrical enclosure is provided for each cell, it is found in practice that roots of each seedling which start horizontally to begin with, soon hit the interior wall of the cylindrical enclosure, curve in and soon form spirals of intertwined roots which will detrimentally affect the growth of the seedling when it grows into a plant or a tree.
It is found expedient to provide vertical rib-like formations on the inside wall of each cell, whereby the roots do not form a spiral tangle; however, such vertical rib-like formations may have an undesirable tendency of directing the roots in directions other than the normal growth direction of the roots. Further, experience has shown that if the side walls of the cells have openings for draining and air admission, any roots that tend to emerge from the openings stop and are virtually pruned by the surrounding air.
In many large-scale reforestation projects, there seems to be a strong trend in favor of what is termed "elevated growing" wherein the underside of the cells is surrounded by air, and the required water for growing is supplied from the top only. The most obvious advantages of such an arrangement, as stated supra, are air admission, ease of drainage of excess water and air pruning of roots.
Reverting to yet another aspect of the geometry of the cells per se, the question as to whether the cell should necessarily have an opening at the bottom (in addition to other side openings for drainage and air admission) is governed by whether the seedlings have a tap root or not. Where the seedlings do develop a tap root, provision of an opening at the cell bottom permits the tap root to grow straight down right at the seedling stage, ensuring fast growth and good endurance against any forces while the seedling grows into a plant or a tree.
In certain situations, seedling cells made of disposable material, e.g., net-like containers, or a degradable organic material, are known to be used, thus obviating the need for removal of the seedling from the cell. These arrangements, however, suffer from severe limitations in general, especially during handling and transportation; furthermore, such disposable cells in themselves are invariably unsuitable for elevated growing without the assistance of auxiliary containers for handling and shipping.
While numerous geometrical shapes and arrangements have been developed to provide several of the aforementioned desirable features in seedling units, it has been found that in the case of reusable seedling units, removal of seedlings along with their root lumps and growth media, without the seedling sustaining any root damage or separation from growth medium, has invariably presented a problem. Accordingly, it is desirable to provide an improved construction which facilitates easy and safe removal of seedlings together with their root lumps from the cells of seedling containers, at the same time retaining the advantageous features discussed supra.